Foam containers for restaurants, schools, hospitals and the like are typically formed by placing a foam sheet between a pair of molds and closing the molds to thermoform a part. If the part requires, for example, a lock for a hinged lid container, a reverse draft or undercut can be formed, but forming a reverse draft or undercut for a lock in the part, particularly foam parts, has been a problem. A reverse draft has been difficult to form in foam containers such as polystyrene foam containers due to an inability to strip the formed part from the tooling while maintaining the desired shape of the reverse draft. For this reason, a continuous thermoforming process for forming parts, with a reverse draft has not been possible. If this problem could be overcome, this would allow for different closure designs in parts, and the development of continuous thermoforming processes for forming foam parts.